1. Field of the Invention
The present invention generally relates to coffee machines. More particularly, the invention relates to espresso machines utilizing prepackaged, ready-to-use filters.
2. Description of the Related Art
Conventional coffee machines utilize filter capsules for use with a brewing unit. Typically, the brewing unit may have two brewing-chamber parts which can be displaced relative to one another and, in a closed position, form a brewing chamber for the filter capsules. Generally, one of the two brewing-chamber parts is connected to a brewing-water heater and is provided with a multiple nozzle.
The filters or filter capsules contain the coffee powder which is required for preparing one portion of coffee (e.g. a cup). Commonly, filter capsules for conventional coffee machines are prefabricated in a ready-to-use form and are packaged individually in a flavour-sealed wrapper.
In order to prepare coffee, a filter capsule, once removed from the wrapper, is introduced into the coffee machine from above, through a slot in the machine housing. The filter capsule is intercepted by suitable means between the two brewing-chamber parts, which are in their open position. The two brewing-chamber parts are then moved into their closed position, in which they enclose the filter capsule between them and seal said capsule with respect to external influences. In this position, a defined quantity of brewing water is forced through the brewing chamber and through the filter capsule contained therein. The resulting coffee is directed, via an outflow tube, into a cup which has been brought into position beforehand. Once the brewing operation has been completed, the brewing-chamber parts are moved apart from one another again, as a result of which the filter capsule drops further downwards into a collecting container provided there.
Conventional machines, as previously described, typically only function reliably with a specific type of filter capsule, i.e., a capsule which is designed for the machine and therefore has a defined size and thickness. However, at least certain variations in thickness would be desirable for the purpose of varying the quantity of coffee powder, and thus the desired strength of the coffee produced therewith.
Conventional coffee machines may also usually be used for preparing superheated steam, in which case the water heater is brought to a higher temperature than would be used for preparing coffee. However, in the known machines, problems arise upon changeover from steam preparation to coffee preparation. Specifically, if coffee is prepared immediately after the steam has been removed, i.e. if one does not wait until the reduced coffee temperature has been reached, the filter capsule is initially subjected to the action of steam which is still located in the flow heater and is very hot and under high pressure. This may result in the filter capsule swelling up and even actually exploding, which means that the entire brewing chamber is affected by soiling and has to be cleaned.